Within the field of memories, there is continuing interest in finding ways to increase the storage density and speed of memories. As the personal use of small devices gains popularity, the memory of this equipment has to be modified to match the function and design of these devices. Particularly, as more and more data needs to be stored in memory, the memory needs to have the capacity and speed to handle such demand.
The discovery of the phenomena of the magnetoresistive (MR) effect and the giantmagnetoresistive (GMR) effect provided significant advancements in the field of memory technology. These phenomena demonstrated that the resistance of multilayer thin films comprised of ferromagnetic layers sandwiching a conducting layer can change significantly depending on the direction of an external magnetic field.
GMR is observed in magnetic metallic layered structures in which it is possible to orient the magnetic moments of the ferromagnetic layers relative to one another. One such type of magnetic metallic layered structure consists of a stack of four magnetic thin films: a free magnetic layer, a nonmagnetic conducting layer, a magnetic pinned layer and an exchange layer. Magnetic orientation of the pinned layer is fixed and held in place by the exchange layer.
By applying an external magnetic field, the magnetic orientation of the free layer can be changed with respect to the magnetic orientation of the pinned layer. The change in the magnetic orientation generates a significant change in the resistance of the metallic layered structures. The resistance of the structure determines the logical value to be stored therein. Disk drives that are based on GMR technology use it to control a sensor that responds to very small rotations of magnetic orientation of the GMR free layer due to magnetization on the disk. However, the present use of this technology in disk drives requires the disk to rotate and head to position on the track to be read, which typically requires on the order of 10 ms. In contrast, the access time of the GMR technology itself is generally on the order of 3-5 ns. The disk drive therefore is not utilizing the full potential of fast response time of the GMR, which could translate into small access time.
A related phenomena is the Magnetic Tunneling Junction, as discussed in U.S. Pat. Nos. 5,835,314 and 5,629,922, where a trilayer structure of a ferromagnet (“FM”)-insulator-FM exhibits increased junction resistance across the trilayer structure when the magnetization of the FM layers is antiparallel to one another as compared to when the magnetization of the FM layers is parallel.
Thus there is a clear need in the industry to develop fast memories which can take advantage of the GMR and MTJ phenomena without requiring the long latency associated with the rotation of a disk drive.